1. Field of the Invention
The present invention relates to a clamping mechanism for an injection molding machine and, more particularly, to the posture maintenance of a moving platen in a clamping mechanism.
2. Description of the Related Art
A clamping mechanism for an injection molding machine is configured such that a movable platen having a movable side fixed thereto is moved in the state in which the posture is maintained in parallel to a stationary platen having a stationary side mold fixed thereto. In particular, a toggle or crank type clamping mechanism is configured such that a rear platen disposed opposite to a stationary platen with respect to a movable platen, in addition to the movable platen, can also be moved in the state in which the posture is maintained in parallel to the stationary platen.
When clamping is released (i.e., locking-up is released) after a mold is clamped in the clamping mechanism, the posture of the movable platen is changed under the influence of a clearance between a pin and a link, which connect the movable platen and the rear platen to each other in a toggle mechanism or the like, a clearance between a tie bar and the platen or the like. Therefore, the parallelism between the stationary platen and the movable platen may be possibly deviated by the amount of such a clearance.
The above-described parallelism between the movable platen and the stationary platen represents the parallelism between the movable side mold and the stationary side mold, which are fixed to the platens, respectively, thereby markedly having an influence on the quality and precision of a molded product. In particular, when moldability of high precision is required, it is important to more accurately keep the parallelism.
In order to adjust the parallelism of the moving platen (such as the movable platen or the rear platen) with respect to the stationary platen,
(1) the moving platen must be rotated about an axis (i.e., a horizontal axis) which is parallel to a base plane on which the moving platen is mounted which is also perpendicular to the moving direction (in other words, an inclination of the moving platen in a vertical direction must be adjusted); and
(2) the platen must be rotated about an axis (i.e., a vertical axis) perpendicular to the base plane, on which the moving platen is mounted (in other words, an inclination of the moving platen in a horizontal direction must be adjusted).
The above-described item (1) can be achieved by adjusting a roller or a slide bearing for supporting the moving platen. However, there is provided no mechanism capable of achieving the above-described item (2).
Japanese Patent Application Laid-open No. 9-262884 discloses that the parallelism between the movable and rear platens and the stationary platen is adjusted by guiding the movable and rear platens by the use of a linear guide device. However, the linear guide device has a complicated structure, thereby arising a problem of an increase in cost of an injection molding machine.